The present invention relates to a multi-media communication terminal apparatus for receiving moving picture data and audio data transmitted via a communication line to reproduce these data, and more specifically to a multi-media communication terminal apparatus capable of performing a special reproduction of moving pictures such as a slow reproducing operation.
A number of pieces of video software for amusement purposes and also educational purposes have been supplied by use of media such as video tapes. In recent years, such amusement/educational video software has been supplied via communication lines, e.g., cable television (CATV) services in response to requests by audience. This type of television service is called "Video On Demand:VOD". Also, a terminal apparatus for receiving video software transmitted via communication lines is called a "multi-media communication terminal apparatus". The video-on-demand is greatly expected for utilizations in various fields, since even when the video software is not individually owned, the desirable video software can be always played.
Japanese Patent Application Disclosure No. Hei 4-324784 discloses a multi-media communication terminal apparatus capable of receiving a specific video software to which the individual subscribers have requested to observe. Usually, a video software supplier called a headend apparatus is employed in a CATV system. A large number of pieces of video software are stored in this headend apparatus. A multi-media communication terminal apparatus called a "settop box" is arranged in each of subscribers. A headend apparatus is connected to a settop box by way of a communication line.
To a settop box, a television set equipped with a display, or a predetermined interface circuit is connected so as to reproduce received video software. In this multi-media communication apparatus, a reception channel of a receiver unit for receiving a channel requested by a subscriber is remote-set by the headend apparatus side. The headend apparatus remote-sets the reception channel of the settop box of the subscriber functioning as an audience requesting source in order to receive such a channel through which the video software requested by the subscriber is transmitted. As a result, a program requested for audience can be transmitted by using an arbitrary empty channel.
In video-on-demand, another request may be issued to perform a special reproduction of video software sent via a communication line, for instance, a slow reproduction, or a pause of video software to reproduce a still image.
On the other hand, Japanese Patent Application Disclosure No. Hei 4-243057 discloses a multi-media communication terminal apparatus capable of reproducing video software in special modes. In this terminal apparatus, a output mode control code representative of information related to a special effect is provided within multi-media data as data about video software, in addition to video data and audio data. The reproducing apparatus reproduces video and audio in accordance with the output mode control code contained in the multi-media data. In response to special reproducing modes demanded by subscribers, various sorts of special reproducing operations can be carried out by rewriting the output mode control codes contained in video software.
In addition to video data for a normal reproducing mode, video data for the special reproducing mode is stored in the storage unit employed in the headend apparatus. When the special reproducing mode is requested from the multi-media communication terminal apparatus such as the settop box, the headend apparatus stops the supply of the video data for the normal reproducing mode, and starts the supply of the video data for the special reproducing mode combined with a time stamp instead of the normal video data. Accordingly, the special reproducing operation can be executed in response to the request issued from the subscriber in this headend apparatus.
In addition to the above-described terminal apparatus in which the video data for the special reproducing mode is supplied from the headend apparatus during the special reproducing operation, there is another multi-media communication terminal apparatus capable of performing the special reproducing operation with employment of the normal video data on the side of this multi-media communication terminal apparatus. For instance, in the multi-media communication terminal apparatus for executing the slow reproducing operation in half the normal reproducing speed, the video data received from the headend apparatus is once stored in the buffer memory, and then the stored video data is read out from this buffer memory in the speed suitable for the slow reproducing operation.
In such a terminal apparatus, the data amount of the video data read from the buffer memory per unit time becomes half of the data amount of the video data supplied from the headend apparatus. As a consequence, when the slow reproducing operation is continued for a time period exceeding a predetermined time period, the buffer memory will be brought into a overflow condition. To avoid this overflow condition, the supply of the video data and the stop of this data supply are sequentially instructed from the multi-media communication terminal apparatus to the headend apparatus. In the multi-media communication terminal apparatus, the remaining amount of the video data stored in the buffer memory is confirmed every predetermined time interval. When the confirmed remaining amount becomes below a reference value, this multi-media communication terminal apparatus requests the headened apparatus to supply a predetermined amount of video data which can be stored in an empty region of the buffer memory.
The above-described prior art owns the following diadvantages. That is, in such a conventional multi-media communication terminal apparatus for executing the special reproducing operation by employing the information such as the output mode control code, the video data having a preselected format capable of storing such specific information must be employed. Therefore, this type of terminal apparatus cannot have the general-purpose function. In another conventional terminal apparatus in which the video data for the special reproducing mode is stored on the side of the headend apparatus in addition to the normal video data, there is another problem that the storage data amount is increased, and thus a total number of pieces of video software which can be provided to the subscribers is decreased.
Also, in another conventional multi-media communication terminal apparatus for performing the special reproducing operation by controlling the data reading speed of the buffer memory, the data remaining amount of the buffer memory must be continuously and periodically confirmed. Therefore, there is another problem that the workload to execute this confirmation process is heavy. Moreover, since the video data is normally coded and compressed, the data amount of the video data required to reproduce a single image is varied. As a consequence, it is practically difficult to judge as to how long the video data can be reproduced by considering the data remaining amount of the buffer memory, which is periodically confirmed. As a result, the data amount must be set to a relatively large amount, which constitutes the reference amount used to issue the request for transferring the subsequent video data by the headend apparatus. Therefore, there is a further problem that the storage capacity of the buffer memory must be increased by taking account of this relatively large reference data amount.